It’s nice to see someone use the correct past tense of “shine”, unlike in the denouement speech in Green Lantern (otherwise a good movie).

Once again I’ll have to suggest that we use the term “world” when we need vagueness. Anything smaller than a (brown dwarf) star, and at least as big as B-612 is a world, no matter its orbit. So “rogue world” works.

“Terminal nebula” is good. Or maybe “expanding nebula” in contrast to those contracting nebulae that actually have something to do with planets.

]]>By: CBhttp://blogs.discovermagazine.com/badastronomy/2011/07/13/tears-of-a-dying-star/#comment-299048
Thu, 14 Jul 2011 21:03:17 +0000http://blogs.discovermagazine.com/badastronomy/?p=34541#comment-299048A “rogue planet” not being a “planet” makes sense to me. A masterless samurai isn’t a samurai anymore, a disbarred lawyer isn’t a lawyer, and so forth. It is simply not the case that if the full description of something contains a word, then that word taken in isolation must also apply.

Oh and I’d call a 5 orders of magnitude difference between objects on either side of the divide to be something ‘recognized’ by nature. It is nature which makes the distinction obvious.

But you are right that they should correct this whole “planetary nebula” nonsense regardless of how it would make older texts even more confusing.

]]>By: chris j.http://blogs.discovermagazine.com/badastronomy/2011/07/13/tears-of-a-dying-star/#comment-299047
Thu, 14 Jul 2011 15:04:30 +0000http://blogs.discovermagazine.com/badastronomy/?p=34541#comment-299047Anchor, i’ve wondered what would be a better term for these nebulae, and “terminal nebula” is a pretty good one that avoids the confusion of the original term and is not too technical.

i recall many years ago, hosting public nights at a local observatory near wichita, and the question would always come up: “why is it called planetary nebula?” the ensuing brief history lesson is a guaranteed turn-off; people came to learn about and see the sky, not some mistake made by someone who wanted to call a planet “george.”

]]>By: Angelo Campanellahttp://blogs.discovermagazine.com/badastronomy/2011/07/13/tears-of-a-dying-star/#comment-299046
Thu, 14 Jul 2011 12:30:30 +0000http://blogs.discovermagazine.com/badastronomy/?p=34541#comment-299046I have been intrigued by planetary nebulae for some years. For my take on these dumbbell-shaped objects, see my site: http://campanellaacoustics.com/ange/index.htm. We need to put our modeling hats on because as far as I can tell, the “industry” isn’t.
]]>By: Anchorhttp://blogs.discovermagazine.com/badastronomy/2011/07/13/tears-of-a-dying-star/#comment-299045
Thu, 14 Jul 2011 00:18:56 +0000http://blogs.discovermagazine.com/badastronomy/?p=34541#comment-299045chris j., I suppose you must be right.

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My pleasure, Greg.

]]>By: Anchorhttp://blogs.discovermagazine.com/badastronomy/2011/07/13/tears-of-a-dying-star/#comment-299044
Thu, 14 Jul 2011 00:07:08 +0000http://blogs.discovermagazine.com/badastronomy/?p=34541#comment-299044Who can blame people for getting confused? I DO blame astronomers for not fixing something this chronically irritating and who instead thought it ever so much more important to wonder if Pluto is ‘properly’ to be considered a planet or not, which merely ended up as a semantic debate over the definition of what should have remained a generic word – namely “planet” – that has now ‘officially’ acquired lots of useless ammended baggage that pretends to specify what nature doesn’t even recognize as a ‘category’! A few months ago rogue planets was big news. Oh, WAIT! They CAN’T be called “planets” under the official definition ratified by the IAU. ‘REAL’ planets must have generally cleared their orbits of other planets and debris. Well, in the emptiness of interstellar space, they ply no orbit around any star and have no material to clear. The definition is not even wrong, or rogue planets aren’t planets.
]]>By: Anchorhttp://blogs.discovermagazine.com/badastronomy/2011/07/13/tears-of-a-dying-star/#comment-299043
Wed, 13 Jul 2011 23:59:29 +0000http://blogs.discovermagazine.com/badastronomy/?p=34541#comment-299043Sam, the term “protoplanetary” isn’t a mistake and I have no problems at all with it. When applied to a young star, it works just fine – as in ‘protoplanetary disk’, or ‘proplyd’ for short).

It can also work in cases where aged stars spawn a ‘new’ circumstellar dust disk, perhaps partially recycled with material from planets that have been absorbed by their host stars as they swelled into red giant-hood and regurgitated in the stellar wind as the core shrunk. If the disk lasts long enough, it is perfectly conceivable that such a renewed dust disk might form a set of essentially second-generation planets – in which case the term “protoplanetary disk” is again reasonable, accurate, and descriptively justifiable. (Planets have been known to orbit collapsed objects such as white dwarfs and even neutron stars).

But we’re talking about “planetary nebula”, which are compact nebulae associated with the outflow of dying stars that have moved off the Main Sequence. In other words, stars that are TERMINAL stage of their lives. Near-death. I loathe the term “planetary nebula” because they do NOT have any explicit association with planets EXCEPT the vague resemblance of some of the spherical types to gas giant planets like Uranus and Neptune as seen through small telescopes, which is how the term originated to begin with during the 18th century.

If the matter simply stood there, it would almost be okay, but the fact is we have since appreciated that ‘planetary nebulae’ evolve and undergo stages of development, so the obvious temptation is to place the qualifier “proto-” in front of “planetary nebula” to indicate a ‘planetary nebula’ in its early formative stage of development. (Like calling a dying man a ‘proto-dead guy’). The resulting “protoplanetary nebula” is the horrible result, since it so obviously invites confusion with the OTHER, far more reasonable use of the term, as in “protoplanetary disks”.

But ‘planetary nebulae’ have nothing to do with planets, per se. Some ‘planetary nebulae’ may well be utterly planetless. Those whose host primaries that DO happen to possess planets (and probably more than half do, if estimates of the prevalence of planets from Kepler is any guide) may well tend to indirectly influence the morphology of the outflow, but such planets are never the direct CAUSE or source of material for the nebula we see.

So, EVEN IF the circumstellar dust disk – however the host star comes by it – DOES survive the dying star’s death throes, and lasts long enough to condense into a planetary system, we face the hideous prospect of astronomers describing a protoplanetary disk within a protoplanetary nebula. Then people will inevitably conclude – MISTAKENLY – that these are objects which are specifically planet-makers. And the silliness starts all over again and we all (teachers, astronomers, etc) have to go through yet another aggravating round of corrective explanations to people and youngsters eager to learn what this stuff is all about, but can’t keep from getting hopelessly confused.

Wouldn’t it be simpler and more clear to speak of a possible protoplanetary disk inside a proto-terminal nebula, with no suggestion that these Stellar Terminal Nebulae are THE PREFERRED places where planets form. If they were, most planets would reside in orbits around white dwarf stars and Kepler would surely not see so many planets and planetary systems around Main Sequence stars!

]]>By: chris j.http://blogs.discovermagazine.com/badastronomy/2011/07/13/tears-of-a-dying-star/#comment-299042
Wed, 13 Jul 2011 23:33:47 +0000http://blogs.discovermagazine.com/badastronomy/?p=34541#comment-299042Anchor, you must have no sense of humor.
]]>By: Sam Hhttp://blogs.discovermagazine.com/badastronomy/2011/07/13/tears-of-a-dying-star/#comment-299041
Wed, 13 Jul 2011 21:48:58 +0000http://blogs.discovermagazine.com/badastronomy/?p=34541#comment-299041@Anchor: Okay, I get how we shouldn’t always call every circumstellar dust disk a “protoplanetary” disk, but how is the term a mistake? If it’s a very young star then shouldn’t it at least be a semi-appropriate designation?

Aussi: While I get that humans eyes would have evolved mainly for daylight and that the distances of interstellar space are so vast as to radically affect surface brightness, if these emission nebulae are powered by intense stellar radiation then I’m assuming that, even on a rouge planet in the heart of M42 one should still be able to see a moderate “halo” around the higher energy stars within the nebula, which may or may not be coloured. Then the planetary nebulae – when they are lit up by the white dwarf’s radiation, shouldn’t one be able to see a little bit of a glow if they were hiding behind a shadow shield, facing away from the dwarf. As for the Carina nebula – is the collective radiation really that strong from 100 ly’s distance? A little sad…I had plans for an epic SF novel which would end with the main characters stranded far from civilization on a small Earthlike world about that distance from the nebula, or at least far enough away to cause it to have a significant appearance in its sky with at least some colour.

]]>By: Greg Fishhttp://blogs.discovermagazine.com/badastronomy/2011/07/13/tears-of-a-dying-star/#comment-299040
Wed, 13 Jul 2011 20:09:32 +0000http://blogs.discovermagazine.com/badastronomy/?p=34541#comment-299040Thanks Anchor! That pretty much covers what I wanted to know and all my follow up questions!
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